ggdark: Dark Mode for 'ggplot2' Themes

Activate dark mode on your favorite 'ggplot2' theme
with dark_mode() or use the dark versions of
'ggplot2' themes, including dark_theme_gray(),
dark_theme_minimal(), and others. When a dark theme
is applied, all geom color and geom fill defaults
are changed to make them visible against a dark
background. To restore the defaults to their original
values, use invert_geom_defaults().